I like the grandma's tactic. While she used it in the country, I hear it works in the city too. A guy at my BJJ school who worked as a private security consultant told me that he advised employees who had to walk to work in anti-2A cities to buy a cup of the hottest coffee at the closest 7-11 or bodega and keep it in their hand on the walk to work. I'd always prefer a firearm, but I can see how a face-full of scalding hot coffee could deter an attack.
I think the guy was way too into coffee. He used to also advise non-confrontational city-dwellers to keep small valuables (watches, cash, jewelry, etc.) in an empty Starbucks cup with a lid on their walk home. He said muggers always take the wallet, but never steal anyone's coffee cup.